1. Field of the Invention
This invention relates to an idle speed control for an engine, and more particularly to an improved idle speed control of an engine that is provided with an idle speed controller (ISC).
2. Description of Related Art
Internal combustion engines generallyxe2x80x94have include air induction systems that supply air charges to combustion chambers. The air induction systems usually comprises a single main air intake passage or a plurality of main air intake passages. Throttle valves are provided therein to control amounts of air supplied to the combustion chambers. The throttle valves are generally operated by throttle control mechanisms such as accelerator pedals for automobiles and throttle levers for outboard motors.
The engines are operated often under no load, i.e., in an idle state. For instance, generally the engines require to be warmed up for a while after started without any load. Also, the operator may wish to stay an associated vehicle or watercraft without stopping the engine operations. Under the idling condition, the throttle valve is closed and hence no air charges are supplied to the combustion chamber through the main air intake passages. In order not to stop the operations, the engines must keep their own idle speeds. The engines, thus, include idle air passages additionally to the main air intake passages in the air induction systems. The idle air passages bypass the main air intake passages and communicate to combustion chambers of the engines as well as the main air intake passages.
In other occasions such as an engine start, warming up or running under very low atmospheric temperature or preventing the engine from stalling when decelerated, the engine needs a larger amount of air than under the usual idle conditions described above even the throttle control mechanism is not operated.
Conventionally, an amount of air supplied to the combustion chamber through the idle air passage to maintain the idle speed is regulated by a mechanical control system. Although the mechanical control system is simple, it is difficult to change air amounts in response to the various conditions. However, as great results of developments in connection with electronic control systems in recent years, an idle speed controller (ISC) is now added to the conventional control systems.
The ISC is a feedback control system. In this system, the idle air passage has an idle throttle valve therein. An actual idle speed is sensed by a crankshaft angle position sensor associated with a crankshaft of the engine. Meanwhile, an electronic control device stores a preset idle speed in its control map. When the actual idle speed is sensed, a signal is sent to the control device and compared with the preset idle speed. If the actual idle speed is greater than the preset idle speed, the control device will activate the idle throttle valve toward the closed position. If the actual speed is smaller than the preset speed, the control device will activate it toward the open position. The actual idle speed is accordingly maintained as almost equal to the preset idle speed. Since the control device can store multiple preset idle speeds, the ISC is quite suitable for controlling the idle throttle valve in the idle air passage under the various conditions.
On the other hand, some engines are provided with a plurality of air intake passages as noted above. Conventionally, an air manifold is provided upstream of the respective air intake passages and a common throttle valve is placed therein. Also, a single ISC is provided on an idle air passage which bypasses the throttle valve. Because this arrangement only has the single ISC, a control method for the ISC is simple. However, it requires, upstream of the air manifold, a relatively large plenum chamber in which air charges to the respective intake passages are coordinated not to interfere with each other.
Another arrangement is proposable. In this arrangement, all of the air intake passages include their own throttle valves therein separately and a plurality of idle air passages bypass the respective intake passages. In addition, each idle air passage is provided with an ISC separately. This arrangement does not need a large space for the abovenoted plenum chamber. However, the multiple ISCs, in turn, require separate controls because intake air pressures in the respective idling air passages are different from each other. Accordingly, separate control maps for the ISCs are necessary in this arrangement.
It is, therefore, a principle object of this invention to provide an engine that has a relatively compact air intake system and an ISC which can be easily controlled.
Also, if an engine has a single ISC for multiple idle air passages, air charge must be collected to the ISC and then delivered to respective combustion chambers. In this arrangement, if the delivered air charges flow rapidly in respective delivery conduits which are placed between the ISC and the respective combustion chambers, they are likely to be irregular relative to each other. As a result, the idle control by the single ISC will be unstable.
It is, therefore, another object of this invention to provide an engine that will not cause any unstable condition of an ISC even it is a single one.
Further, outboard motors, of course, may have engines which incorporate the ISC. When the ISC is incorporated in an outboard motor, another problem appears.
The outboard motor generally comprises a drive unit and a bracket assembly. The drive unit is mounted on a transom of an associated watercraft by the bracket assembly for pivotal movement about a steering axis and also about a tilt axis. The drive unit includes a power head in which the engine is placed, a driveshaft housing depending from the power head and a lower unit further depending from the driveshaft housing. The engine has an output shaft extending generally vertically. The output shaft drives a driveshaft extending generally vertically within the driveshaft housing toward the lower unit. The driveshaft, in turn, drives a propeller shaft extending generally horizontally within the lower unit through a forward, neutral and reverse transmission. The propeller shaft then drives a propulsion device such as a propeller. A shift device is provided to switchover the transmission among a forward, neutral and reverse positions. A large part of current outboard motors employ dog clutches for switchover mechanisms.
If the ISC, for example, malfunctions and increases air amounts that flow through the idle air passages without any limitation, the idle speed becomes so fast that the shift operation from the neutral position to the forward or reverse position and vice versa tends to be difficult or impossible. The switchover mechanism incorporating the dog clutch is likely to cause this accident. Also, the outboard motor is sometimes operated in the forward position with the idle speed. This is a trolling condition and the associated watercraft advances quite slowly. The inconvenience situation particularly has an inclination to happen when the switchover mechanism is operated from the forward position under this condition to the neutral position. If the idle speed exceeds over a certain range, the switchover action will be impossible.
Further, in the event of dislocation or damage of delivery conduits, non-controlled and large amounts of air will be supplied to the combustion chambers. Under this condition, the large amounts of air flow into the combustion chambers and then the idle speed surely exceeds a permissible range and the shift action of the switchover mechanism will become impossible also. The same problem may occur in seizure or damage of the ISC.
It is, therefore, a further object of this invention to provide an engine in which an idle speed will not exceed a permissible range on any occasions.
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder body defining a plurality of cylinder bores in which pistons reciprocate. A cylinder head is affixed to an end of the cylinder body and defining combustion chambers with the pistons and the cylinder bores. A plurality of air intake passages are provided for supplying air charges to the combustion chambers. Each one of the air intake passages includes a throttle valve arranged to control an amount of the air charge that flows through each one of the air intake passages. An idle air manifold is also provided for supplying air charges to the combustion chambers. A feedback control system is arranged to control amounts of the air charges that flow through the idle air manifold based upon a difference between a preset idle speed and an actual idle speed of the engine.
In accordance with another aspect of the present invention, an internal combustion engine comprising a cylinder body defining at least one cylinder bore in which a piston reciprocates. A cylinder head affixed to an end of the cylinder body and defining a combustion chamber with the piston and the cylinder bore. At least one air intake passage is provided for supplying an air charge to the combustion chamber. The the air intake passage includes a throttle valve arranged to control an amount of the air charge that flows through the air intake passage. An idle air passage bypasses the throttle valve to deliver idle air to the combustion chamber. An idle air control system is arranged to control an amount of an air charge that flows through the idle air passage. The idle air passage has a fixed cross-sectional area through which an amount of air is regulated.
In accordance with a further aspect of the present invention, an internal combustion engine comprises a cylinder body defining a plurality of cylinder bores in which pistons reciprocate. A cylinder head is affixed to an end of the cylinder body and defining combustion chambers with the pistons and the cylinder bores. A plurality of air intake passages are provided for supplying air charges to the combustion chambers. Each one of the air intake passages includes a throttle valve arranged to control an amount of the air charge that flows through each one of the air intake passages. An idle air passage bypasses the throttle valves to deliver idle air to the combustion chambers. An idle air control system is arranged to control an amount of an air charge that flows through the idle air passage. The idle air passage includes an idle air manifold having an inlet portion and a plurality of idle air delivery conduits. The idle air delivery conduits diverge from the idle air manifold and communicate with the respective air intake passages. The sum of cross-sectional areas of the idle air delivery conduits is greater than a cross-sectional area of the inlet of the idle air manifold.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.